Baker-Campbell-Hausdorff relations and unitarity of SU(2) and SU(1,1) squeeze operators

For squeeze operators, an alternative to the matrix derivations of Baker-Campbell-Hausdorff relations is presented for the groups SU(2) and SU(1,1). The technique involves the solution of a system of nonlinear, first-order differential equations. By this method, criteria for unitarity of the representations are established, and these apply to both infinite- and to finite-dimensional representations of these groups.